找到特殊字符的第三次出现并在R之前删除所有内容

Question

我有这个包含URL的示例向量.我的目标是获取URL的路径.

sample1 <- c("http://tercihblog.com/indirisu/docugard/", "http://funerariagomez.com/js/ggogle/a201209e3f79b740337b7bdb521630fe/", 
      "http://www.t-online.de/contacts/2015/08/atlas.html/", "http://mgracetimber.ie/wp-content/themes/Banner/db/box/", 
      "http://zamartrade.com/cs/DHL/DHL%20_%20Tracking.htm/", "http://dunhamengineering.com/menu/Auto-loadgoogleDrive/Document.Index/", 
      "http://www.indiegogo.com/guide/forum/2014/09/forgot-password/", 
      "http://raetc.com/wp-admin/Service/clients/votre-compte/en-ligne/imp-rem.fr/", 
      "http://www.lidanhang.com/img/?https://secure.runescape.com/m=weblogin/loginform.ws?mod=www&amp;hwjklxlamp;ssl=0&amp;dest/", 
      "http://www.sudaener.com/wp-includes/js/crop/dropbox/", "https://zeustracker.abuse.ch/blocklist.php/", 
      "https://zeustracker.abuse.ch/blocklist.php?download=hostsdeny/", 
      "https://zeustracker.abuse.ch/blocklist.php?download=iptablesblocklist/", 
      "https://zeustracker.abuse.ch/blocklist.php?download=snort/", 
      "https://zeustracker.abuse.ch/blocklist.php?download=squiddomain/"
    )

我最初的尝试是这样的:

gsub('http://[^/]+/','/',sample1)

但是,这对于具有的URL不起作用https://.一个合适的解决方案是在第三次出现之前丢弃所有内容"/".我想知道如何使用regex这个以及如果有办法使用它substring.

谢谢

Answer 1

gsub因为代码更清晰,更直接,所以最好随身携带.

如果要在第3天之前删除所有内容/,请使用

> gsub('^(?:[^/]*/){3}','/',sample1)
 [1] "/indirisu/docugard/"                                                                              
 [2] "/js/ggogle/a201209e3f79b740337b7bdb521630fe/"                                                     
 [3] "/contacts/2015/08/atlas.html/"                                                                    
 [4] "/wp-content/themes/Banner/db/box/"                                                                
 [5] "/cs/DHL/DHL%20_%20Tracking.htm/"                                                                  
 [6] "/menu/Auto-loadgoogleDrive/Document.Index/"                                                       
 [7] "/guide/forum/2014/09/forgot-password/"                                                            
 [8] "/wp-admin/Service/clients/votre-compte/en-ligne/imp-rem.fr/"                                      
 [9] "/img/?https://secure.runescape.com/m=weblogin/loginform.ws?mod=www&hwjklxlamp;ssl=0&dest/"
[10] "/wp-includes/js/crop/dropbox/"                                                                    
[11] "/blocklist.php/"                                                                                  
[12] "/blocklist.php?download=hostsdeny/"                                                               
[13] "/blocklist.php?download=iptablesblocklist/"                                                       
[14] "/blocklist.php?download=snort/"                                                                   
[15] "/blocklist.php?download=squiddomain/"   

本^(?:[^/]*/){3}场比赛:

• ^ - 字符串的开头
• (?:[^/]*/){3} - 正好3次出现:
  • [^/]* - 除零之外的零个或多个字符 /
  • /- 一个文字/字符.

Cath建议你的正则表达式修正更准确,但也许,你想^在开头添加只在字符串开头匹配:

gsub('^https?://[^/]+/','/',sample1)
      ^     ^

的?(贪婪)量词指一点或零的出现,从而使s后http可选的.它与(但效率更高)相同gsub('^(https|http)://[^/]+/','/',sample1).

你可能还想让你的正则表达式不区分大小写,添加ignore.case = TRUE.